A & E

In a typical American household, you can find four things that absorb or eliminate moisture: towels, silica gel, diaper crystals and dehumidifiers. Let's take a look at how they work, because all four are different.

Let's start with towels. Whether we are talking about paper towels or cotton towels, they are made from cellulose. If you were to take a cellulose fiber and look at it at the atom level, you would see that it is made out of chains of glucose molecules. Yes, your paper towel is really a giant sheet of sugar. But the sugar is chained together in such long strands that it doesn't dissolve in water.

So, what happens when a paper towel touches water? The water moves in and binds to the trillions of sugar molecules locked in the towel. Instead of the sugar dissolving in the water, the water dissolves in the sugar. Because sugar and water have such an affinity for each other, a paper towel can absorb a large amount of water.

Little packets of silica gel are found in all sorts of products because silica gel is a desiccant -- it collects and holds water vapor. In leather products and foods like pepperoni, the lack of moisture can cut down on the growth of mold and reduce spoilage. In electronics, silica gel prevents condensation which might damage the electronics. If a bottle of pills contained any moisture vapor and cooled rapidly, the condensing moisture would ruin the pills. You will find little silica gel packets in anything that would be affected by excess moisture or condensation.

Silica gel is nearly harmless, which is why you find it in food products. Silica, aka silicon dioxide (SiO2), is the same material found in quartz. The gel form contains millions of tiny pores that trap moisture molecules. Silica gel is, essentially, porous sand.

Silica gel can take the relative humidity in a closed container down to about 40 percent. Once saturated, you can drive the moisture off and reuse silica gel by heating it in an oven at 350 degrees.

If you have kids wearing disposable diapers, you are probably familiar with the clear crystals that will sometimes appear on your child's skin. The crystals come from the "super absorbent layer" found in most disposable diapers. This layer consists of paper fluff and a polymer absorbent called sodium polyacrylate.

Sodium polyacrylate is an amazing water absorber -- it can absorb 200 to 300 times its weight in tap water (even more if the water is distilled) and hold it in a gooey gel.

Sodium polyacrylate is a pretty cool polymer. Shake the crystals out of a new diaper (or buy the crystals at a garden center) and add water to them to see how amazing they are. Water binds to each molecule in the polymer strand and the crystals grow. When you see toys that grow to 10 times their original size when placed in water, they are powered by sodium polyacrylate.

Finally there are dehumidifiers. The most common household dehumidifier is a plug-in unit that can pull a gallon or two of water out of a humid room or basement in a day. These are surprisingly simple devices.

Think about a normal room air conditioner that you would put in a window of your home. The air conditioner has two sets of coils -- one hot and the other cold. The cold coils are inside the room, and a fan blows air over them to cool the room. The hot coils are outside the window so the unit can dump heat outdoors.

A dehumidifier is just a room air conditioner like this with both the hot and cold coils inside the room. When humid air hits the cold coils, the moisture in the air condenses and drips into a bucket or hose. Then the dry air flows through the warm coils to heat the air back up. This approach works surprisingly well in a humid room.

The next time you face a moisture problem, you now know of four different ways to tackle it.

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